Tablets not working by the sound of it — get less (4,3)
I believe the answer is:
ease off
'get less' is the definition.
'tablets not working by' is the wordplay.
'tablets' becomes 'ease' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'not working' becomes 'off' (I've seen this before).
'by' says to put letters next to each other.
'ease'+'off'='EASE OFF'
'the sound of it' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
(Other definitions for ease off that I've seen before include "relent" , "Throttle back" , "relieve tension" , "Slacken gradually" , "Let up" .)